Polyurethane elastomer compositions



United States Patent Office Patented Feb. 18, 1969 3 428,598 POLYURETHANE EIJASTOMER COMPOSITIONS Kanji Matsubayashi and Hiroyuki Segawa, Kurashiki,

Japan, assignors to Kurashiki Rayon Co. Ltd., Kurashiki, Japan No Drawing. Filed Aug. 31, 1966, Ser. No. 576,234 Claims priority, application Japan, Sept. 15, 1965, 40/56,557; Sept. 16, 1965, 40/56,831 U.S. Cl. 26045.75 Int. Cl. C08g 51/58, 51/04 5 Claims ABSTRACT OF THE DISCLOSURE Polyurethane elastomers otherwise subject to yellowing upon exposure to heat and atmospheric gases are stabilized by incorporating therewith from 0.01 to by weight, based upon the elastomer, of a sulfur-containing compound selected from the group consisting of wherein m is an integer of from 1 to 5, and n is an integer of from 6 to 30, and from 0.01 to 10% by weight, based upon the elastomer, of titanium dioxide.

This invention is directed to provision of a polyurethane elastomer stabilized against yellowing due to heating and exposure in the air, which comprises a polyurethane elastomer formed by reacting a polyester glycol having hydroxyl radicals on both ends, a diisocyanate, and a low molecular weight diol, blended with at least one compound selected from the group consisting of high aliphatic alcohols containing sulphur atoms, carboxylic acids containing sulphur atoms, carboxylic acid esters containing sulphur atoms in the main chain and mixtures of a phenol derivative and an acid.

It is known that polyurethane elastomers are materially yellowed by heat, light, or by oxidizing components of the air, and the yellowing has presented a serious problem in the application of the elastomers.

For the prevention of yellowing, attempts have hitherto been made to blend polyurethane elastomers with phenol derivatives, amine derivatives or the like 'Which are known as rubber antioxidants, but none of these has satisfactorily solved the problem. Also, it has been proposed to synthesize polyurethane elastomers having good resistance to yellowing by the use of a suitable diisocyanate as a reactive component or of a suitable component as a chain extender of the elastomer. However, most of those components are expensive and inevitably increase the manufacturing cost.

An object of the present invention is to provide polyurethane elastomer compositions stabilized against yellowing due to heating and exposure in the air by blending a polyurethane elastomer composed of polyester having hydroxyl radicals on both ends as a soft segment, a diisocyanate, and a low molecular weight diol as a chain extender with at least one compound selected from the group consisting of higher aliphatic alcohols containing sulphur atoms, carboxylic acids containing sulphur atoms, or carboxylic acid esters containing sulphur atoms, and

mixtures of a phenol derivative and an acid. Compounds wherein an aromatic nucleus is directly bonded to a sulphur atom have proved ineffective as compared with the compounds according to the invention.

Another object of the invention is to achieve the effect of remarkably improving the whiteness of polyurethane elastomers by the addition ofcompounds according to the invention.

Polyurethane elastomers useful in the practice of the invention will be more specifically described hereunder. The polyester glycol for preparing the elastomers has a molecular weight above 500, preferably in the range from 500 to 8,000, and may be a hydroxyl group-terminated polyester obtained by poly-condensation of a dicarboxylic acid such as adipic acid or sebacic acid with an aliphatic glycol such as ethylene glycol, propylene glycol, or butylene glycol, or may be a hydroxyl group-terminated polyester such as poly-caprolactone obtained by ring opening polymerization of lactone.

Organic diisocyanates particularly useful for the invention include naphthy-lene diisocyanate, 4,4-diphenylmethane diisocyanate, and phenylene diisocyanate or 2,4-(or 2,6) tolylene diisocyanate. An aliphatic diisocyanate such as hexamethylene diisocyanate may also be employed.

The diol present as a chain extender may be ethylene glycol, propylene glycol, butylene glycol, pentamethylene glycol, diethylene glycol, tetraethylene glycol, or a diol having a benzene nucleus such as 4,4'-diphenylolalkane. Polyurethane elastomers for use in the invention are made by the reaction of these three components.

The compounds containing sulphur atoms which are to be blended with the polyurethane elastomers according to the invention include sulphur-containing higher aliphatic alcohols having the formula wherein m is an integer of from 1 to 5, and n is an integer of from 6 to 30; sulphur-containing higher aliphatic acids having the formula CH (CH S (CH COOH wherein m is an integer of from 1 to 5, and n is an integer of from 6 to 30; sulphur-containing higher acid esters having the formula wherein m is an integer of from 1 to 5, and n is an integer of from 6 to 30; sulphur-containing higher dicarboxylic acid esters having the formula wherein m is integer of from 1 to 5, and n is an integer of from 6 to 30; and hydroxyl radical and sulphur-containing higher aliphatic acid having the formula HO (CH S (CH COOH wherein m is an integer of from 1 to 5, and n is an integer of from 6 to 30.

Illustrative examples of suitable sulphur-containing higher aliphatic alcohols which may be employed in the invention are ,8(laurylthio-)butyl alcohol, ;3(stearylthio-)butyl alcohol, fl-(caprylylthio-)ethyl alcohol, fl-(caprylthio-)butyl alcohol,

fi-(laurylthio-) ethyl alcohol,

[3- (pentadecylthio-) propyl alcohol, fl-(cetylthio-)amyl alcohol,

3 B-(stearylthio)ethyl alcohol, 13- (-stearylthio-) propyl alcohol, [3- (stearylthio-) amyl alcohol, fi-(-dodecylthio-)propyl alcohol, and [3- (melissylthiobutyl alcohol.

Illustrative examples of suitable sulphur-containing higher aliphatic acids which may be employed in the invention are [3- laurylthiopropionic acid, cetylthioacetic acid,

[3- (caprylylthio-) acetic acid,

,8- caprylthiobutylic acid, fi-(laurylthio-Waleric acid, fi-(stearylthio-)butylic acid,

- (stearylthiovaleric acid, B-(dodecylthio-)acetic acid and fl-(melissylthio-)propionic acid.

propionate, dipentadecyl thiodiacetate, distearyl thiodiace- 9 tate, dimelissyl thiodiacetate and dimelissyl thiodibutyliate.

Illustrative examples of suitable hydroxyl radical and sulphur-containing higher aliphatic acids which may be employed in the invention are w-(B-hydroxyethylthio-)lauric acid,

wfl-hydroxypropylthioundecanoic acid, w- (fl-hydroxyethylthiocaprylic acid,

w- B-hydroxybutylthiolauric acid, w-(fl-hydroxypropylthio-)caprylic acid,

w- B-hydroxybutylthio-) palmitic acid,

w- (/8-hydroxyethylthio-) stearic acid, w-(B-hydroxypentylthio-)stearic acid and w- (fi-hydroxypropylthiomelissylic acid.

The amount of each compound ranges from 0.01 to by weight based on the elastomer, preferably from 0.05 to 5% by weight. The effects achievable by the compounds are enhanced by the addition of titanium dioxide, an ultraviolet ray absorbing agent, and other additives.

Phenol derivatives for use in the invention include phenols in which the 2,4,6-positions are replaced by an alkyl radical, for example, 4-methyl-2,6-ditertiary butylphenol, 2,4,6-tritertiary octylphenol, and 2-methyl-4,6- ditertiary amylphenol; halogen-containing phenol derivatives such as Z-methoxy-methyl-5,6-dichloropheno1 and 2,6 dimethoxy-4-methyl-S-chlorophenol; cresol derivatives such as 2,4-diisopropyl-m-cresol or 2,6-dimethylo-lp-cresol; and bisphenol derivatives such as 4,4'-butyli rivatives are enhanced by the addition of titanium dioxide, an ultraviolet ray absorbing agent, and other derivatives.

The acid compounds suitable for use in combination with phenol derivatives in accordance with the invention are acids, acid anhydrides, halogenated acid derivatives or the like, with an acid ion dissociation constant ranging from 5 10 to 1 l0 preferably from 1X10- to l l0 at C. They include acids such as hydrochloric acid, sulphuric acid, orthophosphoric acid, phosphorous acid, iodic acid, formic acid, acetic acid, monochloroacetic acid or dichl'oroacetic acid; carboxylic acids such as ortho (or meta) chlorobenzoic acid, oxalic acid, maleic acid or salicylic acid; organic sulfonic acids such as benzenesulfonic acid or paratoluenesulfonic acid; acid anhydrides such as sulphuric acid anhydride, sulphurous acid anhydride, phosphorus pentaoxide or acetic anhydride; and acid chlorides such as thionylchloride, sulfonylchloride or paratoluenesulfochloride.

The acidic ingredient is added in an amount of from 0.01 to 5% by Weight, preferably from 0.1 to 2% by weight of the amount of polyurethane elastomer.

The invention is illustrated in the following examples.

Example 1 Hydroxyl radical-terminated polyethylene propylene adipate having a molecular weight of 2,070 (ethylenepropylene copolymerization ratio- 9:1), 4,4-diphenylmethane diisocyanate and ethylene glycol in amounts at a molar ratio of 1.0:5.0:4.0 were allowed to react at 100 C. to obtain a polyurethane elastomer, The elastomer was mixed with 1% by weight of ,8-(laurylthio-) ethyl alcohol and 2% by weight of titanium dioxide, and the mixture was dissolved in dimethyl formamide to prepare a 20% spinning solution. After defoaming, the solu tion was spun into a coagulating bath at C. which consisted of water containing 30% dimethyl formamide. Upon washing with water and drying, polyurethane elastomer filament was obtained. For purposes of comparison, filament containing 2% by weight of titanium dioxide but not the additive according to the invention was obtained in the same manner as above described.

Samples of the filaments were heat treated by drying at 120 C. for 24 hours, and other samples of non-heat treated filaments were allowed to stand for 30 days in a place where they were kept from direct sunlight. From the tints of the samples visually observed and from reflection curves of the samples in the range from 300 to 700 m on a spectrometer, Yellowing Indices (Y.I.) of the samples were calculated on the basis of the reflectance of 480 mg and of the formula,

Y.I. (Yellowing Index) (lRl/ R2) (wherein R1 represents reflectance at 455 mu and R2 represents reflectance at 557 III/L). The Y.I. values thus obtained of the samples with and without the addition of compounds in accordance with the invention were compare-d. The greater the value of reflectance or less dene-bis(3-methy1-6-tertiary. butylphenol), 2,5-bis(2-hy- 60 the Y.I. value, the whiter the sample obtained.

TABLE 1 Untreated After treatment 120 C. for 24 hours After standing in air for 30 days Compound Tint Reflect. Reflect. Tint Reflect.

visually at Y.I. Tint visually at Y.I. visually at Y.I. observed 480 m observed 480 mu, observed 480 my, percent percent percent Titanium dioxide. 2% White 74. 2 3. 9 Light yellow. 53. 4 13. 8 Yellow 47. 5 16. 9 fl-gauryilthzigmthyl alcohol, 1.0%; Titanium d0. 89. 3 1. 6 White 9. 4. 0 White 81. 2 3.8

mm e, 0.

droxy 4 methylbenzyl) 1,4 xylene or 2,2-bis(4-hydroxyphenyl) propane.

The amount of each derivative ranges from 0.05 to 10% by weight based on the elastomer, preferably from 0.1 to 5% by weight. The effects achievable by the dethe invention brings outstanding eifects in remarkably improving the whiteness of the untreated filament and substantially keeping the product from yellowing by heat treatment and exposure in air for a lengthy period of time.

, For purpose of comparison, a mixture containing only 3.0% by weight of titanium dioxide and a mixture containing 3.0% by weight of titanium dioxide and 2.0% by weight of 4,4'buty1idene-bis(3-methyl-6-tertiary butylphenol) were formed into filaments in the same manner Example 2 5 as above described.

Samples of the filaments were heat treated at 120 C. A polyureth ne la Was Ohtalned y fefltitlflg for 24 hours, others were irradiated by Fade-O-Meter y roxyl radlcal-termmated P yp py n adlpate vfor 30 hours and others were allowed to stand in air ing a molecular Weight of 4,4'-dlphenylmethalle m for 30 days in a place where they were kept from direct dllsocyanate, and ethylene glycol at a molar Tatlo of sunlight. After these treatments, the samples were tested 1014-7135 at and 05% dlstearylthlodlploplonate for Y1. and mechanical properties on the basis of the and 0.6% dlo yl p p Were added to the 1 tints as visually observed and the reflectance indices at t In r and miXed th wi The mlXtllre Was n 480 mg and Y1. values calculated from the reflectance lectl'on moulded to a rod-like Shape under Such COIldlcurves in the range of 300 to 700 I'D/L as determined by t n at t e temperature Was and the feSlspectometer. The results are shown in Table 2. Throughdence time of the polymer was four minutes. As comout the experiment, the greater the value of reflectance or pared with the polymer before moulding the product the less the Y.I. value, the whiter the sample obtained.

TABLE 2 Compound Treatment Item determined Titanium Titanium dioxide, 3.0%; 4,4- Titanium dioxide, 3.0%; 4,4-

dioxide, butylidene-bis(B-methyl-fibutylidene-bis(3-methyl-6- 3.0% tert.butylphenol), 2.0% tert.butylphenol), 2.0%;

Acetic anhydride, 0.5%

Tint visually observed White White White Untreated Reflect. at 480 m (percent) 78. 5 70.2 88.6 Y.I 8.8 4.1 2.1 Strength (g./d. 1.35 1.28 1.33 Elongation (percent) 482 408 417 Tint visually observed. Light yellow Light yellow White After heat treatment at Reflect. at 480 111;; (percent) 56. 5 65.3 82. 5 120 C. 1'0124 hrs. Y.I 12.8 12.8 6. 7 Strength (g./d.) 0. 92 1. 08 1. 29 Elongation (percent) 312 364 425 Tint visually observed Dark yellow Yellow White After irrad. with Fade-O- Reflect. at 480 m (percent)- 35. 1 47. 2 78.8 Meter for 30 hrs. Y.I 36. 4 29. 4 7. 7 Strength (g./d.) 0. 51 0. 77 1.17 Elongation (percent) 187 289 496 Tint visually observed Yellow Light yellow White After exposure in air for Reflect. at 480 m (percent) 49. 2 62. 5 80. O 30 ays. Y.I 18.5 14.8 5.6 Strength (g./d.) 1.08 1. 10 1. 25 Elongation (percent) 377 379 410 was slightly yellowed. However, a moulding prepared under the same conditions but without the two sulphur-,

containing esters above mentioned turned yellowish brown,

against yellowing of the melt.

Example 3 Polyethylene propylene adipate having hydroxyl radicals on both ends and a molecular weight of 2,070 (ethylene-propylene copolymerization ratio=9:1), 4,4-diphenylmethane diisocyanate, and ethylene glycol in amounts at a molar ratio of 1.0:5.0:4.0 were reacted at 100 C. to obtain a polyurethane elastomer. The elastomer was thoroughly mixed with 2.0% by weight of 4,4 butylidene-bis( 3 methyl 6 tertiary butylphenol), 0.5% by weight of acetic anhydride and 3.0 by weight of titanium dioxide. Then the mixture was dissolved in dimethyl formamide to prepare a spinning solution which has a viscosity of 1,150 poises at C. After defoaming under vacuum, the spinning solution was extruded through a spinneret having 10 holes each 0.2 in diameter, into a spinning column and dried therein by hot air at 220 C. The dried product was wound up at a rate of 350 m./min., and thus polyurethane elastomer As can be seen from Table 2, the polyurethane composition. according to the invention has a high resistance to yellowing and is also highly resistant to deterioration of the mechanical properties of the product.

It can be further seen that the whiteness of the untreated filament can be remarkably improved by the addition of acid.

Example 4 The same polymer as described in Example 3 was dissolved in dimethyl formamide to prepare a 15% solution.

To the solution, 1.0% by weight of 4-methyl-2,6-ditertiary butylphenol and 0.2% by weight of hypophosphorous acid were added, and the mixture was coagulated in Water to form a film. For comparison, a mixture containing only 1.0% by weight of 4-methyl-2,6-ditertiary "butylphenol, and a mixture containing only 0.2% by weight of hypophosphorous acid, and a mixture containing neither of these additives were formed into films in the same manner as above described. These films were examined for colouring after irradiation by Fade-O-Meter for 30 hours or after exposure in the air in the absence of direct sunlight for 30 days. The results are shown in Table 3.

filament was obtained.

TABLE 3 Compound Treatment No compound 4-rnethyl-2,6-ditert. Hypophosphorous 4-methyl-2,6-ditert. butylphenol, 1.0%;

aci 0.2 o butylphenol, 1.0% Hypophosphorous acid, 0.2%

Untreated White White White White. After irrad. by Fade-0-Meter for 30 hrs" Do. After exposure in air for 30 days Y 11 Do.

It is apparent from the above table that 4-methy1-2,6- ditertiary butylphenol and hypophosphorous acid are not effective when used singly but can exhibit a remarkable effect when used in combination.

Example 5 Hydroxyl radical-terminated polybutylene adipate having a molecular weight of 1,950, 4,4-diphenylmethane diisocyanate and. ethylene glycol at a molar ratio of 1.0:4.7:3.8 were reacted at 100 C. to obtain a poly- 8 What we claim is: 1. Polyurethane elastomeric composition, highly stabilized against yellowing, comprising (A) polyesterurethane elastomer produced from the reaction of polyester glycol having hydroxyl radicals on both ends and a molecular weight of more than 500, diisocyanate and low molecular weight diol;

(B) from 0.01 to 10%, based on the weight of said elastomer, of a sulfur-containing compound selected from the group consisting of the compounds repreurethane elastomer. The elastomer was blended with 1.5% 10 sented f r h f l by weight of 2,5-bis(2 hydroxy 4 methylbenzyl)-1,4- xylene, 0.5% by weight of acetic anhydride and 2.0% Q. CH3(CHZ)S(CH2)OH by weight of titanium dioxide, and the mixture was disit? CH3(CH2)Y1S(CH2)mCOOH solved in dimethyl formamide to prepare 18% solution. (In) CH3(CH2)mS(cH2)mcOO(CHZ)nCH3 The solution was then extruded through a spinneret having 100 holes each 0.08 mm. in diameter and was spun (iv) (GHMOOWCHMOH: into filaments in water at 35 C. containing 30% dimethyl l formamide. For purposes of comparison, 1.5% by weight of 2,5-bis(2-hydroxy-4-methylbenzyl) 1,4 xylene, 0.5% 20 (CH2)mCOO(CHz)nCH; by weight of acetic acid anhydride and 2.0% by weight of titanium dioxide were blended in a 15% dimethyl and formamide solution of a polyurethane elastomer formed of hydroxyl radical-terminated polytetramethylene glycol (v) HO(CH2)ms(CH2)C0OH having a molecular weight of 1,900 as a soft segment, wherein m is an integer of from 1 to 5, and n is 4,4'-diphenylmethane diisocyanate, and p,p'-methylene an integer of \from 6 to and dianiline in the same manner as above described. The miX- (C) from 0.01 to 10%, based on the weight of said ture was wet spun into filaments. The results are shown elastomer, of titanium dioxide. in Table 4. 2. A polyurethane elastomeric composition according In the same way as in Example 3, these two types of 30 to claim 1, wherein the sulfur-containing compound is filaments containing the compounds according to the infl-(laurylthio)ethyl alcohol. vention were tested for colouring on heating, irradiation 3. A polyurethane elastomeric composition according by Fade-O-Meter, and upon exposure in the air. to claim 1, wherein the sulfur-containing compound is As will be clear from Table 4, the use of compounds fi-( y wp p i H according to the invention, that is, combined used of 4. A p y p elastomerw corrgposltlon acwrdms 2,5-bis(2-hydroxy-4-methylbenzyl)-1,4-xylene and acetic claim l p the sulfur-contaming mp 1s anhydride, exhibited little effect against yellowing and dlsteal'yl thlodlpmplonatedeterioration upon irradiation by Fade-O-Meter of the 5. A polyurethane elastomeric composition according polyurethane elastomer in which polyether was as a soft to claim 1, wherein the sulfur-containing compound is segment. 40 dioctyl thiodipropionate.

TABLE 4 Polymer Treatment condition Item determined Polytetramethyleue glyool- Polybutylene adipate4,4'-

4,4-diphenylmethane didiphenylmethane diisocyanate-p,p-methylene isocyanate-ethylene dianiline glycol {Colouring White White Untreated Strength (g./d.) 0.87 1. 24 Elongation (percent)- 682 895 Oolourin Yellow White After heat treatment at 120 0. for 24 hrs .{Streugth (g./d.) 0.66 1.19 Elongation (percent). 650 418 Colouring Dark Yellow White After irrad. by Fade-O-Meter for 30 hrs .{Strength (g./d.) 0. 13 1. 07 Elongation (pe ent 112 348 Colouring Dark Yellow White After exposure in air for 30 days {Strength (g./d.) 0. 58 1. 20 Elongation (percent) 518 389 References Cited UNITED STATES PATENTS 2,915,496 12/1959 Swart et a1 260-457 3,067,149 12/1962 Dombrow et al 2602.5 3,072,605 1/ 1963 Rodgers et al. 260 45.95 3,179,625 4/1965 Ehrhart et a1. 260- 3,193,525 7/1965 Kallert et al. 26045.9 3,280,049 10/ 1966 Hyre et a1. 260-2.5 3,352,822 11/1967 Yamadera et a1. 26048.85

FOREIGN PATENTS 665,356 6/1963 Canada.

DONALD E. CZAJA, Primary Examiner.

V. P. HOKE, Assistant Examiner.

U.S. Cl. X.R. 

